Microsoft adds to a glut of free iOS online storage with SkyDrive app

Microsoft on Tuesday released an app that lets iOS users access its SkyDrive online storage service. This gives owners of the iPhone, iPad and iPod Touch 25 gigabytes to hold documents, files and music.

Twenty-five gigabytes is cool, right? Unfortunately, on the iPhone there are some limitations, largely due to iOS itself. The app is mostly read-only. You can look at files, but not much beyond that. You can move and delete files and share links, but you can’t alter them and you can only upload photos and videos. (A Windows Phone app also released Tuesday has more capabilities, which you’d expect on Microsoft’s own mobile platform.)

Microsoft is not alone in offering free cloud-based storage for phones. On my iPhone, I’ve now got access to 77 GB of storage through apps alone. That doesn’t count what Apple’s own iCloud allows for. And if you count Web-based storage, I’ve got even more.

• Dropbox – The venerable online storage service gives away 2 gigabytes of storage, sharable across multiple platforms: PCs, Macs, Android, iOS and more. On Macs and PCs, its software creates a folder that looks just like all your others, and it’s about as seamless as it gets. You can pay for more – $50 GB for $10/month, 100 GB for $20/month. I find that 2 GB works for me as a quick place to drop files I need to access everywhere, or when I need to share a file with someone quickly.

• Box.net – In mid-October, Box.net offered iPhone and iPad users 50 GB of free storage, for life. It was a promotion for its new iOS app that lasted only 50 days, and I snatched it up. Normally, Box.net offers 5 GB of free storage, with 25 GB for $10 and 50 GB for $20. What’s particularly cool is that its iOS app will let you stream to an AirPlay-compatible devices. That means you can store video or audio on Box.net and then stream to Apple TV, a Boxee Box or device that works with AirPlay.

• Amazon Cloud Drive – Though there’s no iOS app for this yet, you can access Amazon’s storage service via the Mobile Safari Web browser. The accompanying Amazon Cloud Player on the Web works great on the iPad, but can be frustrating to use on the iPhone. You get 5 GB free, but once you buy an album from Amazon’s music store, you’re bumped up to 20 GB free for a year. Music you buy on Amazon doesn’t count against general storage, which can include almost any kind of file. Once the free offer expires, you’ll pay $20 a year for 20 GB. If you don’t pay when your free year ends, you’ll be bumped down to the 5 GB free plan, but the files you’ve uploaded won’t go away – you just won’t be able to access them until you pay up.

• Google Music – This storage service is primarily for music, and wasformally launched last month. It’s aimed at Android and desktop/notebook computer users, but the player also works on Mobile Safari. Google also is now selling music through this service, though its selection isn’t as complete as iTunes or Amazon’s store. You can upload up to 20,000 songs for free. If you figure each song averages about 3.5 MB, that’s more than 70 GB of storage.

Add Amazon and Google’s gigabytes to the mix, and I’ve got more than 160 GB of storage in the cloud, in my pocket, all free. That’s pretty sweet.

There are other services that offer storage to mobile device users. Got one that you particularly like? Share it in the comments.